Pressure equalizing switch device



PRESSURE EQUALIZING SWITCH DEVICE Filed Feb. 17, 1966 80 POROUS MEMBRANE 0 am a 2 m L m mm m N p w m 1..F v M 41 m J u m 2 B T l M G W UA mm v mm .M 3 m m b w \N j 4 T 8 h 6 2 E 7 2).: m & m R Q) M@ a 2 w m 7 N \N 2 m w W Q mm 0m M ATTORNEYS United States Patent 3,349,203 PRESSURE EQUALIZING SWITCH DEVICE Byron F. Wolford, Minneapolis, Minn., assignor to Proximity Controls, Inc., Minneapolis, Minn, a corporation of Minnesota Filed Feb. 17, 1966, Ser. No. 528,123 5 Claims. (Cl. 200-453) ABSTRACT OF THE DISCLOSURE Switching apparatus including a casing having an opening at the front side thereof with porous material stretched tautly thereacross and held fixedly in place, and an imperforate wall of nonmagnetic material substantially parallel to the porous material and spaced therefrom, a first magnet mounted between the porous material and the wall for movement with flexure of the porous material, a second magnet and a switch mounted behind the wall so that movement of the first magnet causes movement of the second magnet and operation of the switch. The porous material is flexed only by particulate matter and unaffected by fluid because of equalization of fluid pressure on either side thereof due to the porosity of the material.

This invention relates generally to electric switches, and pertains more particularly to a switch that will provide an indication of the level or height of particulate or granular matter within a container, yet which will remain passive or inactive with respect to changes in air pressure within the container.

particulate or granular material, i.e., flour, is to be trans mitted to a remote vantage point. On the other hand, grain elevators and other storage containers of this type where material is conveyed pneumatically are susceptible to changes in pressure therewithin which must not cause the switch unit to operate and thus transmit faulty information or provide inaccurate control signals where a control function is to performed. This is also true in dust control systems where dust is drawn off or out of a work area by either a positive or negative pressure, such pressure being capable of activating or de-activating a diaphragm switch.

Accordingly, one object of the present invention is to provide a switch device that will have especial utility in dust-laden environments in that the switch contacts, where sparking or arcing can occur, are completely isolated, being in a sealed compartment or housing, and which switch device will not be actuated by pressure changes within the storage system. More specifically, the invention has for an aim the employment of magnetically actuated switch contacts, there being a porous membrane associated therewith that automatically equalizes on either side thereof so that the pressure differences will not cause the switch device to operate but at the same time such membrane will be flexed by granular material when present to produce the requisite switch operation via the magnetic linkage.

Another object of the invention is to provide a switch device for pneumatic systems of the envisaged character that will not require lengthy conduits or tubes for achieving the pressure equalization.

A further object is to provide a switch device of the foregoing type that will not contribute to or encourage insect infestation within the storage container because of pockets or nesting areas in the ends of equalizing tubes or pipes introduced into the bin above the working level to provide equalizing pressure behind a diaphragm.

The invention also has as an object the avoidance of other problems stemming from the use of conventional flexible diaphragms. For instance, the rod or shaft extending from the diaphragm to the switch mechanism permits air seepage along such a shaft; the present invention obviates such a happening by employing a magnetic linkage. More specifically, when practicing the instant invention, an imperforate wall can be utilized which precludes air flow into the cavity containing the switch mechanism. Also, by eliminating the rod or shaft, as well as any 0- ring seal, there can be no accumulation of dust or other air-laden foreign matter which could interfere with the free movement of such a rod or shaft to cause stickage and the like. Still further, a feature of the present invention is to provide for facile hermetic sealing of the switch mechanism, thereby allowing installation in potentially explosive environments.

These and other objects and advantages of my invention will more fully appear from the following description, made in connection with the accompanying drawing, wherein like reference characters refer to the same or similar parts throughout the several views and in which:

FIGURE 1 is a front elevational view of a switch device shown mounted on the inside of a fragmentarily depicted wall of a grain elevator or the like;

FIGURE 2 is a longitudinal view of the device taken in the direction of line 22 of FIGURE 1, and

FIGURE 3 is a rear View of the device pictured in FIGURE 1 with the back of the casing taken off so as to expose the switch mechanism contained in the casing, and a portion of the front wall having been broken away to show a small circular section of the porous membrane at the front of the device as seen through one of the pressure equalizing apertures provided in the metal plate or disc confronting the back side of said membrane.

Inasmuch as the present invention will have considerable utility in conjunction with indicating the level of bins, hoppers, grain elevators and similar structures, a fragmentary portion of a wall 10 of such a structure has been pictured in FIGURE 1. The unit or device for sensing the level of the material with respect to the height of the wall 10 has been denoted in its entirety by the reference numeral 12. The device 12 includes a casing 14 comprised of an imperforate front wall 16 of non-magnetic material, such as aluminum, brass or appropriate plastic. Integral with the front wall 16 is a cylindrical side wall 18 having an outwardly directed flange 19. The purpose of the flange 19 is to accommodate a plurality of screws 20 which serve to mount the unit 12 against the wall 10. As will be discerned from FIGURE 3, the interior of the casing 14 is provided with several reinforcing ribs 21a, 21b and 210 that collectively have an H- shaped appearance. A removable backing plate 22 closes the rear of the casing 14, there being a plurality of screws 23 that detachably secure the plate 22 in place.

Within the confines of the casing 14 is a bracket 24, one flange of this bracket being aflixed to the inner side of the front wall 16 and through the agency of a couple of mounting screws 26 a switch mechanism 28 is fixedly mounted within the casing 14. The switch mechanism 28 is preferably of the snap-action variety and may be a micro switch. The construction of such switches is well known, but it can be pointed out that they usually include a plastic housing 30 in which a pair of cooperable electrical contacts 32, 33 are located. The contacts 32,

33 are for purposes of illustration shown as normally open with the contact 33 being carried on a snap-action overcenter split spring 34. For the sake of completeness, a pair of interiorly disposed conductors 36, 38 have been illustrated, these conductors leading to respective terminals 40, 42. A reciprocable plunger 44 is utilized to press against the Spring 34 to accomplish the desired snapaction and the concomitant closing of the contacts 32, 33.

Instrumental in effecting the closing of the contacts 32, 33 is an actuating arm 46 formed with integral cars 47 that are apertured for the accommodation of the ends of a pivot pin 48 mounted in a fixed relation with respect to the plastic housing 30 of the switch mechanism 28. A coil spring 50 is positioned between the arm 46 and the housing 30 so that the arm 46 is normally biased in a clockwise direction as viewed in FIGURE 2.

Playing an important role in the practicing of the instant invention is a first permanent magnet 52. The preferred type of magnet to be used in this situation is a ceramic magnet composed of barium carbonate and iron oxide. Not only are magnets of this type quite small for their magnetic strength, but such magnets will not weaken one another when left in each others fields or are positioned in an electrical field, the spring back being almost 100 percent. In addition, this type of magnet has a high electrical resistivity, thereby adding a further desirable attribute to its use in this situation.

The imperforate front wall 16 has already been referred to. At this time, attention is called to the fact that a recess r pocket 54 is formed in this wall so as to minimize the thickness of the wall 16 in the region of the magnetic field associated with the magnet 52. Anchored at one end to the outer surface of the front wall 16 is a leaf spring 56. A pair of screws 58 provide the anchoring action and a screw 60 permits adjustment to be made of the leaf spring with respect to its flexibility. The screw 60, as can be seen from FIGURE 2, is threadedly carried by the spring 56 and abuts at one end against the wall 16.

A second permanent magnet 58, which is identical to the previously-mentioned magnet 52, is mounted at the free end of the leaf spring 56. Up to this point, nothing has been said concerning the pole arrangement of the magnets 52, 58, which are in the form of rectangular wafers. It will be understood that every permanent magnet has both a north and south pole. It is intended that the magnets 52, 58 be magnetized in the direction of their pressing. This causes a flux concentration to exist near each end of the magnet and on one face thereof. It is further intended that the two magnets be mounted with their magnetized faces nearer each other and with their like poles directly opposite. Hence, by reason of the fact that like magnetic poles repel each other, there is a strong magnetic field produced that causes the two magnets 52, 58 to be urged apart. Hence, when the magnet 58 is moved toward the imperforate wall 16, there is a magnetic field that acts upon the magnet 52 to repulse the magnet 52 and thereby move the actuating arm 46, and consequently the plunger 44, with the result that the spring 34 is deflected in such a way that the contact 33 carried thereon is moved into engagement with the contact 52. Preferably, the magnets 52 and 58, which are in the form of rectangular wafers as above indicated, are secured to the arm 46 in one instance and the leaf spring 56 in the other by a suitable adhesive, such as an epoxy resin. The point to be appreciated, though, is that similar or like poles of the two magnets 52, 58 are oriented in a direction so that the magnetized faces thereof reside nearer the opposite faces of the imperforate wall 16 with like poles thereof directly opposed to each other.

As can be seen from FIGURE 2, the imperforate wall 16 is formed with an annular flange 60 having an outer inclined portion 62 and an inner shoulder portion 64. A bezel or retaining ring 66 is attached to the flange 60 by screws 68, the heads of these screws residing within the casing 14 but accessible by removing the backing 4 plate 22 when the unit 12 is detached from the wall 10 by first having removed the screws 20. For a purpose described below, the retaining ring 66 is formed with a complemental inclined portion 70.

The invention contemplates the use of a porous membrane 72 that overlies and covers the opening in the annular flange 60. The membrane 72 is in the form of fine mesh fabric woven with polyester (Dacron) or polyamide (nylon) fibers, both of which plastic materials are somewhat resilient. These fabrics are currently available, being used in the milling industry for filtering purposes. More specifically, their characteristics are as follows:

It is the inclined portion 70 of the retaining ring 66 that engages the marginal portion of the porous membrane 72 in order to anchor the membrane to the casing 14 in a normally planar or flat condition. In other words, the membrane 72 extends tautly over the front opening, but due to the resiliency or stretchability of the individual fibers constituting the membrane, the membrane can deflect when the front face thereof is subjected to particulate matter stored in the container defined by the wall 10.

A metallic backing plate or disc 74 is adhered to the rearwardly directed face of the membrane 72, Close inspection of FIGURE 2 will show that the plate or disc 74 is somewhat smaller in diameter than the membrane, resulting in its being supported solely by the membrane. Additionally, the plate or disc 74 is formed with a number of apertures 75. The apertures 75, along with the annular portion of the porous membrane 72 not cov ered by the plate 74, allow fluid pressure to be equalized very readily through the membrane 72 due to its woven construction. The porous nature of the membrane is such, however, that the flour or other particulate matter bearing against the forwardly directed face (the side opposite the side to which the plate or disc 74 is attached which is the left side in FIGURE 2) will not pass through the membrane, due to its fine mesh, but instead will cause deflection thereof from its normal or planar state. In other words, the mesh of the membrane will be selected so that it will act as a barrier to the size of particles constituting the stored material, yet will freely allow air (or whatever fluid is employed in the particular pneumatic system) to pass for the purpose of equalizing the pressure on both sides of the membrane. Should the force from the stored granular material become sufficiently great, the edge of the plate or disc will strike or abut shoulder portion 64 and thus prevent damaging forces from being applied to the membrane 72, the magnet 58 or the leaf spring 56 on which the magnet is mounted.

For the purpose of indicating when the contacts 32, 33 have been closed in the above-explained manner, a pair of conductors 76, 78 are shown attached to the previously-mentioned terminals 40, 42. As can be seen from FIGURE 3, the conductors 76, 78 extend upwardly through a coupling 80 which is connected to a conduit or pipe 82. The conduit or pipe 82 is mounted in place against the wall 10 by reason of a U-shaped clip 84 and mounting screws 86.

Continuing with the portion of the description pertaining to the manner in which the contact closing is indicated, it will be observed from FIGURE 1 that the conductors 76, 78 have in circuit therewith a disconnect switch 86 which will first be closed so that a battery 88 and a signal light 90 are connected in series when the contacts 32, 33 are actuated into engagement with each other. In other words, the light 90 will be energized whenever the material in the bin has reached the height of the unit 12 mounted to the wall of such bin.

Although only one unit 12 has been illustrated, this particular unit indicating only when the bin has been completely filled, it will be understood that additional such units 12 can be mounted at lower elevations on the wall 10 and that similar circuitry will signify when the level within the bin has reached predetermined lesser heights. For instance, it might be desirable to indicate when the bin is one-quarter full, one-half full and threequarters full plus the full indication shown in the accompanying drawing.

Having presented the foregoing information, the manner in which my switch device operates should be readily understood. Assuming that there is a change of air pressure within the grain elevator or other container formed by the wall 10 and on the inside of which my device 12 is mounted, this pressure will be quickly equalized due to the porosity of the membrane 72 (more specifically via the sections of fabric overlying the apertures 75 and that annular portion circumjacent the edge of the plate or disc 74) so that no deflection thereof takes place. Consequently, the switch mechanism 28 remains unactuated and no spurious information or signal is transmitted; in other words, in the illustrative installation the lamp 90 remains de-energized.

While the switch mechanism remains passive or inactive due to changes in fluid pressure, such is not the case when granular material builds up to a height suflicient to cause deflection of the membrane 72. The lateral load applied by such material readily deflects the membrane 72, the polyester or polyamide fibers thereof yielding or stretching enough to allow this, with the result that the plate or disc 74 moves rearwardly or to the right as viewed in FIGURE 2.

Owing to the pole arrangement of the magnets 52, 58, a repulsive magnetic field is created which results in the inner magnet 52 being urged farther into the confines of the casing 14 whenever the leaf spring 56 is deflected sufficiently. Whenever the magnet 58 is retracted or withdrawn, though, the magnet 52 is immediately permitted to return to its normal position, this being the position depicted in FIGURE 2, by action of the expanding coil spring 50. Inasmuch as the magnet 52 is carried on the switch actuating arm 46, the plunger 44 will close the contacts 32 and 33, doing so through the split spring 34. This occurs whenever the magnet 58 is moved rearwardly or to the right in FIGURE 2 by sufficient fleXure of the membrane 72.

It will be appreciated that the casing 14 can be hermetically sealed so that there is no likelihood whatsoever of a spark igniting a dust-laden atmosphere or other explosive atmosphere. Consequently, the unit 12 is completely safe in all respects and performs a very worthwhile purpose when used in conjunction with containers of various sorts for particulate and granular materials. On the other hand, there will never be any faulty operat tm o e i h mec a s 25 due o s a g in fl id pressure. In this latter regard, it will be appretiated that no lengthy tubes need be installed which lead to portions of the storage container where ingress of particulate matter is not apt to occur, for the porous membrane 72 ohviates such a need. When my device 12 is installed in a grain elevator, this is an important saving of time and materials because such containers are usually very large. Further, my device 12 is such that no vulnerable ledges, openings, etc. exist where insect infestation is encouraged, this being an important attribute where flour is being handled.

It will, of course, be understood that various changes may be made in the form, details, arrangements and proportions of the parts without departing from the scope of my invention as set forth in the appended claims.

What is claimed is:

1. A pressure equalizing switch device comprising:

(a) casing means having an opening at the front side thereof;

(b) porous material extending across said opening and attached to said casing means so that said porous material is maintained in a generally taut, resilient condition;

(c) a switch mechanism contained in said casing means and including a first magnet movable by said porous material and a second magnet movable by said first magnet, said second magnet causing operation of said switch mechanism when said first magnet is moved rearwardly by deflection of said porous material due to pressure applied thereto by particulate matter; and

(d) said switch mechanism remaining unoperated when only fluid pressure is applied to said porous material due to the equalization of fluid pressure at both sides of said porous material.

2. A pressure equalizing switch device as set forth in claim 1 including in addition a backing plate having one face thereof secured to the rearwardly directed side of the porous material, the periphery of said plate being disposed radially inwardly of the casing means so as to be supported solely by said porous material.

3. A pressure equalizing switch device in accordance with claim 2 including stop means for arresting rearward movement of said backing plate.

4. A pressure equalizing switch device in accordance with claim 1 including an imperforate wall of non-magnetic material between said magnets.

5. A pressure equalizing switch device in accordance with claim 4 in which said imperforate wall defines a portion of a sealed chamber in which a portion of said switch mechanism including circuit completing means is disposed.

References Cited UNITED STATES PATENTS 5/1911 Frasier ZOO-61.21 5/1963 Scholz 20083 

1. A PRESSURE EQUALIZING SWITCH DEVICE COMPRISING: (A) CASING MEANS HAVING AN OPENING AT THE FRONT SIDE THEREOF; (B) POROUS MATERIAL EXTENDING ACROSS SAID OPENING AND ATTACHED TO SAID CASING MEANS SO THAT SAID POROUS MATERIAL IS MAINTAINED IN A GENERALLY TAUT, RESILIENT CONDITION; (C) A SWITCH MECHANISM CONTAINED IN SAID CASING MEANS AND INCLUDING A FIRST MAGNET MOVABLE BY SAID POROUS MATERIAL AND A SECOND MAGNET MOVABLE BY SAID FIRST MAGNET, SAID SECOND MAGNET CAUSING OPERATION OF SAID SWITCH MECHANISM WHEN SAID FIRST MAGNET IS MOVED REARWARDLY BY DEFLECTION OF SAID POROUS TERIAL DUE TO PRESSURE APPLIED THERETO BY PARTICULATE MATTER; AND (D) SAID SWITCH MECHANISM REMAINING UNOPERATED WHEN ONLY FLUID PRESSURE IS APPLIED TO SAID POROUS MATERIAL DUE TO THE EQUALIZATION OF FLUID PRESSURE AT BOTH SIDES OF SAID POROUS MATERIAL. 